1. Field of the Invention
The present invention relates to an inference processor for performing inference processing by executing production rules and, more particularly, to an inference processor designed to realize high-speed inference processing by choosing a production rule or rules which can be applicable in the next step beforehand in each step of the inference processing.
2. Description of the Related Art
In such a system for executing inference processing by using production rules, a single production rule having conditions matching data associated with a current state provided in inference processing and also matching a conclusion drawn in the course of inference is extracted from a large number of production rules. A final conclusion is drawn by using these extracted rules. In order to realize high-speed inference processing, it is effective to extract a rule applicable in the next step at high speed in each step of inference processing.
Japanese Patent Disclosure (Kokai) Nos. 60-72031 and 62-19940 disclose conventional systems of quickly extracting such production rules. In these conventional systems, condition and conclusion parts of each production rule are checked so that relationships representing a conclusion obtained by execution of which conclusion part satisfies which condition in the next step, i.e., relationships indicating application of which specific rule enables application of a specific rule in the next step, are prepared as a table or a network. In inference processing, a rule applicable in the next step is sequentially selected by referring to these relationships, thus realizing high-speed inference processing.
In these systems, however, since only application relationships between rules are prepared, only the speed of processing for selecting a rule or rules applicable in the next step can be increased. If a plurality of rules are selected, it is impossible to know which is the optimal rule. Therefore, knowledge associated with a general direction of inference concerning, e.g., whether or not a certain state leads to a specific state, or which rule should be applied to draw a certain conclusion from a certain state, and with a global structure of a search graph cannot be obtained. For this reason, an unnecessary rule may be executed, and it is difficult to further increase the speed of inference processing.